Shock absorber for electric contacts



April 29, 1958 J. PARSTORFER 2,832,853

SHQCK ABSORBER FOR ELECTRIC CONTACTS Filed NOV. 5, 1954 2 Sheets-Sheet 1 gmmg April 1958 J. PARSTORFER 2,832,853

SHQCK ABSORBER FOR ELECTRIC CONTACTS Filed NOV. 3, 1954 2 Sheets-Sheet IN VEN TOR. JOHN Pmesrae F52 snocn snsonnnn son ELECTRIC CONTACTS John Parstorfer, Philadelphia, Pa assignor to I-T-E Circult Breaker Company, Philadelphia, Pa, a corpora tion of Pennsylvania Application November 3, 1954, Serial No. 466,610

7 Claims. (Cl. 200-23) My invention relates to shock absorbing means for bodies under impact and is more particularly directed to a shock absorber for mechanical rectifier contacts.

The shock absorber of my invention may be applied to the type of mechanical rectifier disclosed in copending application Serial No. 301,880, filed July 31, 1952 and Serial No. 331,467, filed January 15, 1953, assigned to the assignee of the instant application.

Electrical cooperating contacts which engage at relatively high speeds develop a large amount of kinetic energy. This kinetic energy "is usually dissipated in bouncing when the contacts engage. The problems associated with bouncing electrical contacts are discussed in the following with respect to mechanical rectifier contacts.

A mechanical rectifier produces direct current by making bridging contact between a proper phase of an A.-C. system and the associated 'D.-C. system during the timer interval the particular phase of the A.-C. system is capable of delivering energy in the desired direction and breaking the bridging contact when the A.-C. phase reverses its voltage in relationship to the D.-C. voltage. This operation is performed sequentially and repeatedly in synchronism with the A.-C. frequency.

Mechanical rcctifiers utilize a commutating reactor, which is a non-linear or saturable type reactor, to step the current when it passes through zero value. This operation is fully described in co-pending application Serial No. 212,917, filed February 21, 1951. During the period of each stepping operation either contact engagement or disengagement must be completed. Hence, in a three phase mechanical rectifier conversion unit it is necessary for the contact assembly to make and break the circuit 216,690 times per hour in a 60 cycle system.

It is therefore apparent that contact assembly is a vital component of the conversion unit and must be designed to contribute directly to the quality of conversion performance. Co-pending application Serial No. 307,024, filed August 29, 1952 is directed to the contact time adjustment for the contact assembly, co-pending application Serial No. 438,465, filed June 22, 1954 is directed to a guide means for the movable bridging contact, and the instant application is directed to a shock absorbing means for the cooperating contacts.

The cooperating contacts of a mechanical rectifier are contained in a removable and replaceable contact block in which a helical spring is mounted for biasing the bridging contact into engaged or make position with the stationary contacts.

When the cooperating contacts of a mechanical rectifier come into engagement during the period of the stepping operation of the commutating reactors, the excess kinetic energy developed by the bridging contact is dissipated in a bouncing engagement. That is, after the initial engagement, the bridging contact bounces off the stationary contacts, does work in moving against the bias spring thus decreasing its kinetic energy. The

States Patent M Patented Apr. 29, 1958 bridging contact then recloses, rebounces and loses more kinetic energy, and this process continues until all of the kinetic energy of the bridging contact has dissipated.

A first serious problem introduced by bounce is excess contact Wear in that the random bouncing between t..e bridging contact and the stationary contact will generate much silver dust.

The silver dust is undesirable for two reasons; first, it reduces the mechanical life of the contacts, and, second, the silver dust may form into a chain, one end of which might adhere to the moving contact when it opens while the other end might rest on the stationary contact. Should this be the case, the metallic connection between the moving contact and the stationary contact will not be broken when it is supposed to be and a strong current will flow through the silver chain during the non-conducting cycle of the contacts resulting in a backfire which will shut the machine down and cause damage to the backfiring contacts as Well as adjacent contacts.

Furthermore, each bounce means that the contact must interrupt the relatively high step current of the commutating reactor and remake on this relatively high current. This is not necessary in the operation of the mechanical rectifier and merely serves to double or triple the number of operations the contact must make in a given time, thus decreasing contact life.

A second serious problem connected with bouncing mechanical rectifier contacts is that the bounce may last long enough to finally bounce out of the low current step of the commutating reactor. That is, the contact is still bouncing after the commutating reactor allows the current to increase. Under these conditions, the contact may reopen and reclose on so high a current as to destroy the contacts.

A third problem introduced by bouncing contacts in mechanical rectifiers is that they upset control circuits which depend upon the exact length of time a contact is opened or closed. Copending application Serial No. 494,496, filed March 15, 1955 assigned to the .assignee of the instant application, shows just such a control circuit.

Accordingly, it is a distinct disadvantage to have cooperating contacts bounce upon engagement.

In the prior art arrangements, the helical spring biased the cooperating contacts into engagement but operated under high compressional forces in an attempt to suppress bounce when the cooperating contacts engaged. However, Working a spring under these conditions decreases its life considerably, and backfires due to broken contact springs are common in mechanical rectifiers. Furthermore, even the very high compression of the spring still does not completely suppress bounce.

With my novel shock absorber, the bias spring only biases the bridging contact into engagement. Hence, the bias spring operating compression can be greatly reduced thereby increasing its life.

My novel device provides a shock absorber which will absorb engaging kinetic energy of the movable contact, dissipate the energy and reset for the next operation automatically and rapidly and with a minimum of rebounding torce regardless its rapid operation.

In principle, my novel device provides a means whereby the kinetic energy of the moving contact mass is almost instantaneously transferred to a plurality of movable units having difierent natural frequencies of oscillation which are arranged to dissipate the transferred energy. The movable units are then rapidly reset in sequence to their previous position for the next operation. By resetting in sequence, the average rebounding force of the movable units is much less than if the movable units would be simultaneously reset.

Although this novel shock absorber is discussed primarily in connection with mechanical rectifier contacts, it could be applied to the contacts of an electromagnetic rectifier as well. In fact, this novel shock absorber has a universal application wherever there are bodies in im pact.

Accordingly, it is a primary object of my invention to provide a shock absorbing means to absorb the kinetic energy developed in engaging contacts.

Another object of my invention is to provide a shock absorber that will reset rapidly with a small rebounding force.

Another object of my invention is the provision of a shock absorber made of several independent units, each unit having a different oscillating frequency.

Still another object of my invention is to provide a shock absorber consisting of two units, each unit having a diflerent mass.

Another object of my invention is to provide a shock absorber for a pair of cooperating members that will operate no matter how the cooperating members engage. That is, the shock absorber will operate whether the cooperating members engage with both surfaces parallel or if they engage with the surfaces at random angles to one another.

Another object of my invention is to provide shock absorbing action by means of individual segments, each one of which is in engagement with the body under impact, each of the individual shock absorbers dissipating part of the transmitted kinetic energy by angularly rotating around a common segment fixed to the body under impact.

Another object of my invention is to provide shock absorbing action by means of individual segments, each one of which is in engagement with the body under im pact, each of the individual shock absorbers dissipating part of the transmitted kinetic energy by moving linearly away from the body under impact.

A still further object of my invention is to provide a shock absorber for cooperating contacts in which the total effective movable mass and the coefficient of restitution of the shock absorber and the eiiective movable mass and the coeflicient of restitution of each of the cooperating contacts are all approximately the same.

These and other objects of my invention will be apparent from the following description when taken in connection with the drawings in which:

Figure 1 is a schematic diagram of a mechanical rectifier to which my novel shock absorber arrangement can be applied.

Figure 2 is a perspective view of the mechanical operating mechanism illustrating the manner in which my novel shock absorber can be assembled into the system.

Figure 3 is a cross-sectional view of a mechanical rectifier contact assembly and illustrates my novel shock absorber associated with the stationary contacts.

Figure 4 is a detailed perspective view of my novel shock absorber for a echanical rectifier contact.

Figure 5 is a cross-sectional view of a mechanical rectifier contact assembled with my novel shock absorber having the cooperating contacts in an open position.

Figure 6 is a cross-sectional view of a mechanical rectifier contact assembled with my novel shock absorber showing the motion of the shock absorber segments immediately after contact engagement.

Figure 7 shOWS a cross-sectional view of a second embodiment of my novel shock absorber.

Figure 8 shows a cross-sectional view of the embodiment of Figure 7 immediately after engagement of the cooperating members.

Figure 9 shows a cross-sectional view of a third embodiment of my novel shock absorber.

Figure 10 shows a detailed top view of the shock absorber of Figure 9.

Figure 11 shows a cross-sectional view of Figure 9 immediately after engagement of the cooperating members.

In Figure 1, the source of alternating current is derived from the A.-C. voltage source which energizes the conductors 10, passes through the circuit breaker 11 to the step down transformer 12. The current is subsequently passed through commutating reactor 13 to step the current for commutating purposes as set forth in copending application Serial No. 212,017, filed February 12, 1951. The construction of the commutating reactor is described in co-pending application Serial No. 301,880, filed July 31, 1952.

The current then passes through the disconnect switches 14 to the contact assemblies 15 and 16 which form the subject matter of the application. 'The contact assemblies 15 and 16, which are sequentially operated and are in synchronism with the frequency of the source, are connected to the AC. source buses 10A, B and C to the direct current load buses 20 and 21.

For purposes of simplification, I have shown in Fig ure 2 the mechanical switching arrangement which is utilized for phase A, it being understood that the switching apparatus for phases B and C are identical in construction. my novel shock absorber is assembled in the contact assembly.

The upward movement of the push rod 47 will urge the disc shaped bridging contact 31 upward against the bias of the helical spring 51 and thereby disengage it from engagement with the stationary A.-C. contact 28 and the positive D.-C. stationary contact 26 and shock absorbers 17 and 18. During this period of time the push rod 46 is in its lowermost position and hence the bridging contact associated with the structure 10A is biased into contact engagement by the helical spring associated with the contact assembly 16.

My invention is directed to a novel shock absorbing means that will allow a contact such as the bridging contact 31 to engage contacts such as 25 and 27 without initial bouncing and later rebound due to the shock ab sorber resetting itself.

in Figure 3 I have shown a cross-sectional view or a contact block assembly such as 15 illustrating the manner in which the shock absorbing means is positioned with respect thereto. The contact assembly 15 is comprised of a housing 50, which has a box like form and is preferably made of an insulating material. A helical spring 51 is mounted within the housing between the bridging contact 31 and the spacer 52. The spacer 52 is provided to obtain the proper tension of the helical biasing spring 51 and may be made of brass.

The shock absorbers 17 and 18 and the stationary contacts 26 and 23 are secured to the housing by means of assembly screws 53 which are passed through an opening 54 within the housing 50 which communicates with the upper end thereof, as best seen in Figure 2. Each of the four openings 54 receive an assembly screw 53.

The housing 50 is provided with a lower portion 55 and 56 which serves as a guide spacer for the guide means 60. As best seen in Figures 4 and 5, the guide means 60 described in copending application Serial No. 438,465, filed June 22, 1954, is provided with holes 57 which communicate with the openings 5 when the guide means is positioned between the guide spacers 55 and the housing 50.

The shock absorber 17 and 18 and stationary contact 26 and 28 each are provided with two sets of threaded openings to receive the threaded ends of the assembly screws 53. Hence, when the contact block 15 is assembled as illustrated in Figure 3, the assembly screws 53 serve to position the guide means 60, hold and maintain the guide spacers 55 and 56 and hold and maintain the stationary contacts 26 and 28. Thus, the arrangement This figure illustrates the manner in whichprovides for means to fasten an area of the surface of the shock absorbers 1'7 and 18 to a corresponding area of the stationary contacts 26 and 28. The remaining surface between the shock absorbers 17 and 18 and the stationary contacts 26 and 28 are intimately engaged but are free to separate in a flexing motion.

My invention is directed to the novel shock absorbers 17 and 18 which have a portion maintained to an area of the contacts under impact 26 and 28, all points on the shock absorbers being angularly rotatable about their individual maintained areas.

The shock absorbers l7 and 18 are made of low electrical resistivity material. For best operation, the effective movable mass of the shock absorbers 17 and li and their coefficient of restitution, the total effective mass and coefficient of restitution of the movable contact 31, and the mass of the volume of the stationary contacts 26 and 2d transmitting the kinetic energy and their coefiicient of restitution should be approximately equal.

Figure 4 shows a detailed view of shock absorber 17. Holes 61 and 62 receive the assembly screws 53 which maintain the area around these holes to the stationary contact 26 of Figure 3. Slots '63 through 67 are cut in the body of the shock absorber thus providing individual segments as through 71. Each of the individual segments are attached to the body of the shock absorber 17 which acts like a common segment. The individual segments o d-71 are cut with difierent dimensions in order to impart a difierent natural frequency of oscillation to each segment.

Figures 5 and 6 show a motion picture of the operation of the shock absorber 17. When the contact 31 is in the open position, as shown in Figure 5, the individual segments 68-'71 of the shock absorbers 1'7 and it; are in intimate engagement with the fixed contacts 26 and 27. That is, the natural position for the individual segments is to be flush with the fixed contacts.

Figure 6 shows the condition immediately after contact engagement. In closing, the movable contact 31 develops a certain kinetic energy. Immediately upon engagement, this energy is transmitted through the stationary contacts 26 and 28 and to the shock absorbers 17 and 18. in order to dissipate the kinetic energy, the segments of the shock absorber 6871, 68--7 1' move away respectively from the stationary contacts 26 and 28 and do work by moving against the restoring force due to the elastic nature of the material. Hence, the movable and stationary contacts engage Without bouncing since the energy of engagement has been transferred to a movable unit (the shock absorber segments).

When the shock absorber segments 6871 move away from the stationary contacts 25 and 28, they do so at different frequencies due to their different dimensions. In Figure 6, segment 63 has a higher natural frequency than any of the others, hence, it reaches the peak of its oscillation before any of the others. Accordingly, while segments 6%, 7t and 7t are still moving away, segment 58 automatically begins to return to the stationary contact. Then segments 69, 7t and 71 return to their previous positions in sequence. Therefore, by giving the segments difierent dimensions, they reset in sequence. Hence, the average rebouncing force of the shock absorber is greatly reduced since only a small part of the shock absorber is reset at any instant. If all of the segments oft-71 were to rebound at the same instant, their energy would be transmitted to the movable contact 31 thus causing a bounce. By proper design, the shock absorber can be completely reset in as short a time as is desired.

This novel shock absorber also protects against bounce it the movable bridging contact 31 of Figure 5 is nonparailel to the stationary contacts 26 and 2 8 at the instant of engagement. Under this condition, the individual segment under the immediate area of initial contact would ilex thus keeping the edge of the bridging contact 31 from bouncing away from the stationary contact. The

aseasss bridging contact 31 will then pivot around the area of initial contact and under the influence of the biasing spring and come into flush engagement with the station ary contact 26. Upon the flush engagement, the remaining segments will flex away thus absorbing the remainder of the energy of the movable contact. Thus, my novel shock absorber eliminates a see-saw type of bounce when the cooperating contacts engage at a skew angle.

Furthermore, since the spring 51 does not have to suppress bounce any longer, its operating compressional force can reduced considerably and spring breakage is reduced accordingly. This is a very important advantage since a broken spring will cause the mechanical rectifier to backfire thus causing considerable damage to associated equipment.

This shock absorber can be applied according to the description above to the contact structure disclosed in copending application Serial No. 558,350, filed January 10, 1956, assigned to the assignee of the instant application, as well as the contact assembly of Figure 3.

The above mentioned embodiment of my novel invention has the shock absorber segments angularly rotating about a common segment. Another embodiment of this principle could have the shock absorber segment move linearly away from the body under impact. This type of embodiment of my novel shock absorber is shown in Figure 7.

in Figure 7, 71 is a member under impact, 81 is the impacting member, 82 and 83 are two units in intimate engagement with member 80, and $4 and 85 are biasing means for units $2 and 83. The figure shows the biasing means as a spring but this could be gravity, electromagnetic, hydraulic or any other means of biasing. The arrow labelled F represents a driving means to engage the bodies 80 and 81.

Figure 8 shows the embodiment of Figure 7 immediately after the engagement of members 80 and 81. The shock absorber S2 and 83 absorb the kinetic energy of member 81 which is transmitted through the members so. in order to dissipate the energy, the shock absorbing units 82 and 83 move away from their position of intimate engagement and against the biasing force 32 and 83. Thus, the cooperating members 86 and 31 engage without bounce.

The shock absorber units 82 and 83 and their respective biases 34 and are constructed to have a different naturai frequency of oscillation. This can be done by mismatching the masses S2 and 83, or mismatching the biases 84 and 85, or a combination of both. Hence, the combination having the highest natural frequency will reset, or come back to position of intimate engagement with the member under impact first, and the com-- bination having the lowest natural frequency will reset next.

By utilizing a controlled sequence of shock absorber reset, the average rebounding force of the shock absorbers 83 and 82 on the impact member 80 is considerably reduced.

Furthermore, the average rebounding force of the shock absorber upon the impact member can be made as small as desired by increasing the number of shock absorbing units.

Another disadvantage my novel shock absorber overcomes is the seesaw type bounce which would occur if the members 8% and 81 are not parallel to each other before engagement. For example, in Figure 7, if the left hand side of member 81 engaged the member 80 first, this side would bounce away. Then the right hand side of member 81 would engage member 80 and bounce away, and so on. Using my novel invention, if the left hand side of member 31 engaged member $0, the kinetic energy of engagement will be transmitted to unit 82 immediately under the impact area. Instead of bounc ing, the left hand side of member 81 will remain engaged to member 80, and under the influence of the driving force F, member 81 will pivot about the engaged left hand side and the surface of 81 will engage the surface in a flush manner. Upon this engagement, the energy will be transmitted to shock absorber 83, which will move to dissipate the transmitted energy.

Figure 9 shows still another embodiment of my novel shock absorber. This figure is the same as Figures 7 and 8 except that the shock absorber 86 takes a new form. A top view of the shock absorber 86 is shown in Figure 10. Number 87 of Figure 1 is a hole to take a fastening means such as bolt 38 of Figure 9. in the embodiment of Figure 9, an area of the shock absorber is maintained in engagement by some means which could be the unit and bolt arrangement shown in the figure. The segments 89 and '90 of Figure 10 are normally engaged to the member 80, but upon impact of member 81 upon member 31?, segments 89 and 90 will rotate about the area of maintained engagement as shown in Figure 11, and due to their elastic properties, will automatically reset themselves. The engagement will be substantially bounceless since the kinetic energy of the engagement is transmitted to the segments 89 and 9-0 and they dissipate the energy in their motion. Once again, the segments have a different natural oscillating frequency due to different dimensions, hence the average rebounding force will be decreased.

in the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principle of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appending claims.

.i claim:

1. A pair of cooperating members having an engaged and disengaged position; means to move said cooperating members to said engaged and disengaged position; a shock absorbing means consisting of a plurality of segments fastened to a common segment; said common segment maintained on one of said cooperating members; each of said plurality of segments positioned to be in en agement with said last mentioned member and angularly rotatable about said common segment.

2. A pair of cooperating members having an engaged and disengaged position; means to move said cooperating members to said engaged and disengaged position; a shock absorbing means consisting of a plurality of segments fastened to a common segment; said common segment maintained on one of said cooperating members; each of said plurality of segments positioned to be in engagement with said last mentioned member and angniarly rotatable about said common segment; at least one segment having dimensions to make its natural frequency of angular rotation about said common segment dilferent from the natural frequency of angular rotation any other segment.

3. A pair of cooperating members having an engaged and disengaged position; means to move said cooperating members to said engaged and disengaged position; a shock absorbing means consisting of a plurality of segments fastened to a common segment; said common segment maintained on one of said cooperating members; each of said'plurality of segments positioned to be in engagement with said last mentioned member and angularly rotatable about said common segment; at least one segment having a mass to make its natural frequency of oscillation different than the natural frequency of osn of any otter segment.

4. A pair of cooperating members having an engaged and disengaged position; means to move said cooperating members to said engaged and disengaged position; a shock absorbing means consisting of a plurality of seg ments fastened to a common segment; said common segment maintained on one of said cooperating members; each of said plurality of segments positioned to be in engagement with said last mentioned member and angularly rotatable about said common segment; at least one segment having a mass to make its natural frequency of oscillation different than the natural frequency of oscillation of any other segment; said plurality of segments constructed to move away from said engaged position to said last mentioned member and automatically return to said location in a sequence given by said natural oscillating frequency of each individual segment.

5. A pair of cooperating members having an engaged and disengaged position; means to move said cooperating members to said engaged and disengaged position; a shock absorbing means consisting of a plurality of segments fastened to a common segment; the total mass of said plurality of segments and the mass of each of said cooperating members being approximately the same; said common segment maintained on one of said cooperating members; each of said plurality of segments positioned to be in engagement with said last mentioned member and angularly rotatable about said common segment; at least one segment having a mass to make its natural frequency of oscillation different than the natural frequency of oscillation of any other segment; said plurality of segments constructed to move away from said engaged position to said last mentioned member and automatically return to said location in a sequence given by the natural oscillating frequency of each individual segment.

6. In combination; a first contact; a second contact movable into and out of engagement with said first contact; means for moving said second contact into and out of engagement with 'said first contact; a member having a first and second segment connected thereto; said first segment having a different mass than said second segment; said first and second segments being normally posi tioned adjacent to said first contact; said first and second segments being flexibly movable out of engagement with respect to said first contact.

7. In a mechanical rectifier having a bridging contact and a first and second stationary contact; biasing means to maintain said bridging contact in electrical engagement with said first and second stationary contact; a push-rod assembly to move said bridging contact against said biasing means to thereby disengage said bridging contact from said first and second stationary contact; a first and second segment associated with a first common member and a third and fourth segment associated with a second common member; said first and second segments being positioned to engage said first stationary contact; said third and fourth segments being positioned to engage said second stationary contact; said first segment having a mass difierent than said second segment; said third segment having a mass different from said fourth segment; each of said first and second segments and said third and fourth segments being flexibly movable out of engagement with respect to said first and second stationary contacts respectively.

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